Television system



June 22, 1937. v. K. zwoRYKlN TELEVISION SYSTEM Filed Dec` 24, 195o 4 Sheets-Sheet 1 om l Dm. a. n n 0 U E .INVENTORI adlmlrKZwor'g Kin,

J f v /f/.s ATTO/:NEM

bm: e @Dow June22, 1937. v. K. zwoRYKlN Y 2,084,364

TELEVISION SYSTEM Filed nec. 24; 1930 .4 sheets-sheet 2 Figa.

V. K. ZWORYKIN TELEVISION SYSTEM 4 Sheets-Sheet 3 Filed Deo. 24, 1950 June 22,` 1937.

June 22, 1937. v. K. ZWORYKIN 2,084,364

TELEVIS ION SYSTEM Filed Deo. 24, 1950 4 Sheelzs-SheerI 4 I N VEN TOR A TTORNEY.

Patented June 1937 UNITED STATES 'rELEvrsIoN srs'rEM N g .Vladimir n. zworykin, magnet-.lain J.,- as-f signor, by mesne assignments, to Radio C orporation of America, New York, N. Y., a corporation of Delaware Application December 24,1930, sei-iai No. 504.559 s claims.v (ci. '17a-s) My invention relates to improvements in television systems and apparatus therefor.

y In television receiving systems proposed heretofore. and in which a cathode ray tube. of the general type disclosed in my copending application Serial No. 407,652, led Nov. 16, 1929, is utilized, the received picture impulses are impressed on the grid of the tube to control the intensity of the ray in accordance withconditions of illumination of -the individual spots or regions making up the object at the transmitter. The electrons making up the ray move from the cathode, and pass through a relatively small aperture in the control grid to the so-called rst anode of the tube, from whence they are directed toward a uorescent screen at the larger end of the tube. 'I'he electrons are caused to travel from the cathode to the rst anode at a relatively high velocity, which is increased or stepped up to a muchhigher velocity by a second anode which,

for this purpose, has in some cases been maintained at a positive potential of about 4,500 volts, the rst anode, in such cases, being maintained at a positive potential of about 1,000 volts. The

o relatively high voltage gradient along the axis of the tube between the cathode and the rst anode,

`corresponding to conditions whereat the potential on the first anode. is maintained at about 1,000

volts, has heretofore made necessary the provision for relativelyhigh voltages on the grid to control the` cathode ray completely, the voltage variation lying in a range between 30 and 45 volts.

For the purpose of providing forthese relatively Ihigh grid-control voltages. it has been necessary to utilize high gain audio ampliers in the radio receiver. 'I'hese ampliers are expensive, and, furthermore, operate to distort the received picture appreciably. A

40 In the various constructions of cathode ray tubes used heretofore in television receiving systems, the maximum effect or inuence of the electrons making up the cathode ray has not been effective with respect to the uorescent screen to develop the light image. 'I'his is attributed to substantial leakage of electrons from the cathode to the second anode, around the rst anode. That is, in these cathode ray tubes constructed heretofore, the electrons, after passing through the control grid,have a more or less pronounced tendency to depart from their path of travel in the ray and take a new path of travel around the iirst anode instead of passing through the4 anode aperture for eiectiveimpact with the fluorescent screen.

With the `:foregoing in mind, it is one of the objects of my invention to provide an improved television system ofthe general character referred to, and apparatus therefor, wherein the grid voltage for complete control of the cathode 5 'ray is substantially lower than that required in the various systems proposed heretofore, the grid voltage in the present improved system being sufliciently low to permit direct connection of the control grid with the radio receiver and the asso- 10 ciated radio-frequency amplier, thereby obviating the high-gain, expensive and troublesome audio ampliers requiredin the systems of the prior art. -4

Another object of my' invention is to provide an l5 improved television system, of the general character referred to, wherein the cathode ray tube, forming part of the system, functions as its own detector of the incoming modulated carrier wave to supply'picture impulses to the control grid.' 20 and, if desired, to supply simultaneously the synchronizing impulses to the electromagnetic or other means for causing the ray to scan the uorescent screen structure.

Another object of my invention is to provide an 25 improved television system of the general character referred to, which has advantages over the various systems proposed heretofore in the way of simiplicity, cost of manufacture and electro control. 30

the electrons for the purpose of developing the light image on the fluorescent screen.

Other objects and advantages will hereinafter 40 appear.

In accordance with my invention, the voltage gradient along the axis of the cathode ray tube.

from the cathode to the rst anode, is made to vary, the arrangement being such that the voltage 45 gradient is relatively-low at the region where the electrons pass through the aperture in the control grid, thereby permitting of complete control of the'ray by an input voltage substantially lower 50 than has been `possible heretofore.

More particularly, in accordance with my invention, an auxiliary anode, .in the form ofan apertured shield maintained at a positive poten-g. tial substantiallybelow that of the anode of the 55 electron projector, is interposed between this anode and the control grid of the projector.

My invention resides in the features of construction, proportionment. arrangement and combination of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawings, wherein Figure 1 is a diagrammatic view of a television receiving system embodying the present improvements, one of the parts being shown on an enlarged scale in sectional elevation;

Fig. 2 is an enlarged fragmentary view, partly broken aw-ay, of the smaller end of a cathode ray tube forming part of the present improved television system;

Fig. 3 is an enlarged fragmentary view taken from Fig. 1;

Fig. 4 is a graphical representation of the voltage gradient along the axis of cathode ray apparatus constructed and operated in accordance with my invention;

Fig. 5 is a view similar to Fig. 3, showing a modiiication;y

Fig. 6 is a section taken on the line 6-6 in Fig. 5;

Fig. '1 is a view similar to Fig. 3, showing another modification;

Fig. 8 is a graphical representation of characteristics of operation of cathode ray apparatus constructed and operated in accordance with my invention; and n Fig. 9 is a diagrammatic, fragmentary view,

showing a modification.

With reference to Fig. 1, the cathode ray tube IIl is provided at the smaller end thereof with an electron projector of the general type disclosed in my copending application referred to,

and including a cathode II and a heating filament I2 therefor, an anode I3, and a control grid I4 interposed between the cathode and the anode. The anode I3 of the electron projector is commonly referred to as the first anode of the cathode ray tube.

The filament is supplied with heating current by a battery I5 under control of an adjustable resistance I6. f

For the purposeof controlling the intensity of the cathode ray in accordance with the received picture impulses, the grid I4 is connected by a lead I1 to an output lead I8 from a suitable lter I9. `eiective to filter out the picture impulses from a receiver 20 which includes a radio-frequency amplifier of usual type. The other output lead 2I oi. the filter terminates, as shown, at an adjustable contact 22 of a resistance 23 connected across a battery 24. By adjusting the contact 22, the relation between the potentials on the cathode Il and grid I4 may be varied to suit particular requirements.

It will be understood that the picture signals are transmitted on a carrier wave at a suitable frequency, and that' the synchronizing impulses are transmitted with the picture frequencies on a carrier wave at a frequency beyond the band of picture frequencies. The filter I9 is a. highpass iilter adjusted to pass to the iilter 33 only the carrier wave modulated by the horizontal and vertical synchronizing impulses. The picture signals and the carrier wave modulated by the synchronizing impulses at 16 and 1,000 cycles, for example, are impressed across the resistance 3| by the'connections I8 and 2l from the filter u I9. The carrier wave modulated by the synchronizing impulses is demodulated in the usual manner by a demodulator which may be considered as being associated with the lter 33. The horizontal and vertical frequencies are then filtered one from the other by the filter 33 and 5 utilized to synchronize the usual generators of saw-tooth current waves, which may also be considered as being associated with the filter 33. This part of the receiving system per se forms no part of my present invention, and is dls- 10 closed in more detail in my copending application referred to.

The resistance 24a connected across a battery 25 is provided with an adjustable contact 26 connected to the anode I3 by the connection l5 21, the contact being adjusted to impress the desired positive potential on the anode.

The tube IIl is provided with a second anode in the form of a silver or other metallic coating 28 on the interior of the tube. The second 20 anode 28 operates to accelerate the electrons in their movement from the rst anode I3 to the screen 29, and, also, causes the electrons to come to a good focus on the screen.

The desired positive potential is impressed on 25 the second anode 28 by a battery 30.

A suitable grid leak 3| may be connected across the leads I8 and 2I from the filter I9.

The cathode ray is caused to scan the screen 29 by causing, for example, a saw-tooth cur- 30 rent wave at 1,000 cycles to pass through the coils 34, and a saw-tooth current wave at 16 cycles to pass through the coils 36.

The system thus far described is of the same general type as that disclosed in my copending application Serial No. 484,309, led September 25, 1930.

Coming now more particularly to the structural and electrical characteristics of my improved system to which are attributed the advantages 40 referred to over the Various systems proposed heretofore, reference is made to Figs. 2 and 3. An auxiliary anode, in the form of an apertured disc or shield 38, is interposed between the grid I4 and the iirst anode I3, and is supported and 45 insulated from the grid by a plurality of wires 39 having their adjacent ends connected by glass beads 40, the other ends of these wires being connected respectively to the grid and shield by spotwelding, or in any other suitable manner. The 50 iirst anode I3 is also supported from the grid I4, and is insulated from and held in spaced relation to the shield 38 by wires 4I having their adjacent ends connected by glass beads 42, the other ends of these wires being spot-welded to 55 the shield and first anode, respectively.

The assembly, comprising the grid I4, the iirst anode I3, and the shield or auxiliary anode 38, is supported from the press 43 by wires 44 and 45 secured to the grid in any suitable manner such 60 as by spot-welding. The wire 44 extends entirely through the press 43, as shown, for convenient connection with the lead I1.

In like manner, the cathode II is supported from the press 43 by the wire 45a extending 65 through the latter for connection with the lead 46.

The heating filament I2 is connected across and supported from the adjacent ends of the wires 41 and 48, which also extend through the press 43 for connection with the leads to the 70 battery I5 and the resistance I6.

Connection is made with the anode I3 by the wire 49, which may be spot-welded thereto at the point 49a, which wire extends through a glass or other suitable insulating tube 50, and thence outaos-1,364

and operates to insulate the Aanode connection 49, which is at a relatively high potential, from the shield 38 and grid I4 which are at relatively low potentials.

A skirt or protective shield, in the form of a lotube 52 of `nickel or other suitable material, may

be placed over thatportion of the glass tube 50 on the grid side of the auxiliary anode 38, and

may be welded or otherwise secured to this anode.

The shield or auxiliary anode 38 is connected to the positive side of a battery or other direct current source 53 by a lead 54 connected to a wire 55 extending through the end wall of the tube and spot-welded or otherwise electrically connected to this anode at a. point 56.

In a television receiving system embodying the present improvements, and with which are ob'- tained the advantages referred to, the diameter of the grid aperture 51 is approximately .085 inch, and the diameter of the auxiliary anode aperture 58 and the first anode apertures 59 is approximately .055 inch. In this system, the distance between the grid I4 and the auxiliary anode 38 is approximately .03 inch, the distance between the auxiliary anode 38 and the rst anode I3 is approximately .09 inch, and the inside diameterof the small end of the tube I0 is approximately two inches. While these various dimensions are found to provide for satisfactory operation, it is to be understood that the same are not critical in any strict sense of the word, and may .bevaried within wide limits to suit different conditions.

In the system referred to, the battery 38 is such as to place the second anode 28 at a positive potential of 4,000 volts, the contact 26 is adjusted to place the rst anode I3 at a positive potential of 1,000'volts, and the battery 53 is such as to .place the shield or auxiliary anode 38 at a positive `potential of volts. With this varrangement or adjustment, a negative potential of approximately 45 3.5 volts is effective to completely out off the ray.

In explaining the operating principle of my present improved system, reference is made to Fig, 4, wherein the values of accelerating voltage on the cathode beam are plotted against distance along the axis of the tube from the cathode II to the rst anode I3. With the cathode I I at zero potential, and the shield or auxiliary anode 38 at a positive potential of 45 volts, the voltagegradient along the axis of the tube at the region where the electrons pass through the aperture' 51 in the control grid I4, at which region the electrons will be under the controlling'influence of the grid, is expressed as I `increases sharply to a relatively high value as a result of the relatively great difference in potential between the shield and the rst anode I3. Beyond the first anode I3, the voltage gradient is increased still further by reason of the high positive potential of 4,000 volts on the second anode 28.

From the foregoing it will be seen that the voltage gradient along'the axis of the tube is increased in steps between the cathode II and the first anode I3. The relatively low velocity of the electrons, corresponding to conditionsunder which the voltage gradient is leaves the electrons highly sensitive or responsive to control at the relatively low voltage on the 'grid I4, while the subsequent stepping up of the velocity of the electrons causes them to strike the fluorescent screen 29 at a tremendous velocity, the force of the impact being so high thaty the light or luminescence produced is ample for the development of an image of suillcient brilliancy.

Assuming that the shield or auxiliary anode 38 is ineffective or removed from the tube structure, it will be apparent from Fig. 4 that the voltage gradient along the axis of the tube between the cathode II and the rst anode I3 will be constant and represented by the slope Q ds of the broken line AB. Other conditions remaining the same in the system referred to, it will now require a negative potential as high as 35 volts to completely cut off the ray, and an A. C. input potential of about 12 volts to completely control the ray. For the purpose of obtaining this relatively high control voltage, it would be necessary to employ in the receiving system a high-gain audio amplifier, as heretofore.

A Without the shield or auxiliary anode 38, therefore, the ratio of the first anode potential of 1,000 volts to the negative potential of approximately 35 volts on the control grid I4 for complete cut-oil` of the beam, is about 29, whereas this ratio in my present improved system, employing the shield 38, is substantially greater, and equal to the character described wherein the ratio of the operating electrical potential on the irst anode I3 to the negative potential on the grid for complete cut-ol of the beam, is at least 35, or between and 500.

Considering the operating characteristics of my' present improved system from another aspect, I believe myself to be the rst to provide a television receiving system of the character described wherein complete control of the ray is obtained by input voltages within the range of from 2 volts to 10 volts.

While denite values of potential on the control grid. I4 and the anodes I 3, 28 and 38 have been given, it is to be understood that this has been done only for the purpose of teaching the art operating conditions in a television receiving system constructed and adjusted in accordance with my invention, and not with the intention of limiting myself in the appended claims to these particular values. On the contrary, it is contem plated to vary these values of potential within wide limits to suit different operating conditions and requirements.

In the modification shown in Figs. 5 and 6, the

anode I3a, corresponding to the anode I3 in Figs.

2 and 3, has an apertured base element 60 arranged transversely of the directionof travel of the ray and extending outwardly, as shown, beyond the body portion of the anode into close proximity to the interior wall of the tube. The anode I3a--60 is supported from the control grid I4 by the wires 6I having their adjacent ends connected by the glass beads 62. The shield 38a, corresponding to the shield 38 in Figs. 2 and 3,

l5 is supported from the grid I4 by the wires 63 and the interposed glass beads 64, and is of substantially smaller diameter than the anode base 60.-- This construction permits of direct connection of the anode lead 49 with the outer edge portion of the base 60, Without the necessity of this lead passing through and being insulated from the shield 38a, as in Figs. 2 and 3. It is to be noted that the wires 6I and the associated glass beads 62`for supporting the anode element 60 from the grid I4', are disposed entirely on the cathode side of this element. This construction eliminates the possibility of such supporting means interfering with focusing of the electrons to a small spot on the screen 29.

The construction in Fig. 7 is substantially the same as that in Figs. 5 and 6, except that the shield 38h, corresponding to the shield 38a, is of the same diameter as the anode base 60. The 3 anode is secured to the shield sab by bolts 65 and 66 which pass through an interposed spacing ring 61 of soapstone or other suitable insulating material. The anode lead 49 in this construction may beconnectedto the bolt 65, and the lead 55 to the shield 38h may be connected to-the bolt 66, forv which purpose the bolt 65 is in electrical contact with the base 60 and insulated from the shield 38h, while the bolt 66 is in electrical contact with the shield and insulated from the base 60.

It is to be noted that in the construction shown in: Figs. 2 and 3, the shield 38 has va diameter only slightly less than that of the neck of the tube I0, so that the shield extends well out beyond the anode I3 into close proximity to the wall of .the tube. This construction is believed to contribute materially toward more eicient-shielding of theV anode I3 by the shield 38, which appears to give the tube such desirable characteristics that the same can function as its own detector when embodied in a television receiving system asvshown in Fig. 1.

Withreference more particularly to the wide range, of voltages possible on the control grid I4, the ilrst anode I3, the second anode 23, and the shield or auxiliary anode 38, Fig. 8 shows the characteristics of a cathode ray tube constructed in' accordance with my present invention, and lwhich is identifled as No. |81. In this figure, the curves`68, 69, 10, 1I and 12 were obtained by plotting on the vertical axis the current in the .connection 13 from the second anode 28, and by plotting on the horizontal axis the D. C. polarizing 'voltage onthe grid I4. The curves 68 to 12 showthe characteristics of the tube with the potentials Es of the Ashield or auxiliary anode 38 at 50, 70, 80, and 120 volts, respectively.

'f lDuring the tests made for the purpose of obtaining the necessary data for'these characteristic curves, the resistance I 6 was adjusted so that 75 the supply voltage Ef for the filament was 2.5

,ceases volts, under which condition the lament current If was 2.22 amperes. The vpotential Ear on the first anode I8 was 600 volts, and the potential Ea: on the second anode 28 was 2,400 volts.

With the shield potential Es at '70 volts, the D. C. polarizing voltage on the control grid i4 was found to be best, for this particular tube, at about 1.5 to 2.0 volts, as indicated by the grid voltage line 14. Under these conditions, the voltage variation on the control grid for complete control of the beam, would lie approximately within the range from 1 volt positive to 4.5 volts negative.

With the shield potential Es at volts, the bias on the control grid I4, for this particular tube, was found to be best at about 5 volts. Under these conditions, the -voltage variation on the control grid for complete control of the beam, would lie approximately within the range from zero to 10 volts negative.

With the shield potential Es above 110 volts, for example at volts, as shown by the curve 12, the maximum illumination of the screen 29 was less than the illumination at conditions as represented, for example, by the curves 69, 10 and 1I, and corresponded to a second anode current of about 6.6 microamperes.

The reason for this is due to the fact that, with the shield potential as high as 120 volts, there is only a relatively small increase in the second anode current during the periods of time the grid I4 swings in a positive direction, because the limit of electron emission from the cathode has been reached. This phenomenon is illustrated by the curve 12, from which it will be seen that at a grid potential of about 2.0 lvolts negative, the curve bends sharply into an almost horizontal slope. On the other hand, it will be seen from the curves 69, 10, and 1I, for example, that for lower values of shield potential, the slope of the characteristic curve is relatively sharp throughout the entire operating range of the grid voltage variation.

The data obtained in the tests referred to indicates that for the particular tube tested, having approximately the dimensions given above, most eflcient operation is to be obtained by an adjustment or arrangement whereat the potential on the shield or auxiliary anode 38 is 100 volts, and the bias on the control grid I4 at about 4 to 6 volts negative, with a variation in the picture impulse potential within a range of 8 to 10 volts for complete control of the beam. Under these conditions, the cathode ray apparatus operates on the straight-line portion of the curve, and, accordingly, functions as an amplifier, in which case a suitable detector is interposed between the R. F. amplifier and the apparatus I0 to rectify the picture modulations on the carrier wave.

On the other hand, it will be seen from the characteristic curves of Fig. 8 that if the grid bias is so selected that the lower bend of the curve is utilized, rectication, due to assymetric conduction, will take place in the control grid circuit. This inherent rectifying action places the desired signal voltage upon the control grid in a manner identical to that of an external detector. The control grid I4 is then connected directly to the output of the R. F. amplifier, no external detector being required. That is, in Fig. 1, the connections I8 and 2I would connect directly with the connections shown between the receiver 26 and the filter I9.

The degree of brightness, and character, generally, of pictures received with cathode ray apparatus constructed in accordance with my present invention is substantially better than the degree of brightness and general character of the pictures received with such apparatus constructed heretofore. This is partly attributed to the effect or influence of the shield or auxiliary anode in substantially eliminating electron leakage between the cathode and second anode. The shield or auxiliary anode in the present improved construction, therefore, assures substantially maximum efficiency in the way of complete utilization of the electrons for the purpose of impact with the fluorescent screen 29 to develop the light image.

An important function of the shield 38 isl that substantially all of the lines of electrostatic strain, which would otherwise exist between the grid I4 and the anode I3 under operating conditions, terminate on the shield, which is at substantially ground potential for alternating current. This shield 38, therefore, substantially eliminates capacity coupling between the grid and anode, so that any `effective impedance appearing in the rst anode circuit will not be reflected into the control grid circuit of the tube I Il. Therefore, when my improved cathode ray tube is used in place of a detector following the R. F. amplifier, the shield 38 prevents the effect of increased input capacitance due to reflected plate impedance, which would otherwise occur.

Furthermore, when a radio-frequency circuit feeds the tube I0, the overall gain from the antenna to the control grid I4 is considerably greater than would be the case if shield 38 were not present.

Fig-9 shows a modification of the System in Fig. 1 in which the cathode ray tube not only functions as its own detector of the picture impulses, but also simultaneously detects the synchronizing impulses for the deilecting coils 34 and 36. For this purpose, the bias on the grid I4 is such that the tube operates on the lower bend of the characteristic curve. No external detector is required. The filter I9 is omitted, and the leads I8 and 2i connected directly to the R. F. amplifier contained in receiver 20. A resistor 15, `shunted by a suitable by-pass capacitor TI, is connected as shown in the return lead 21 from the first anode I3. The two leads 32, previously connected to the filter I9, are now connected to the leads 16 from the ends of resistor 15. With these modifications of the system in Fig.` 1, the detected picture and synchronizing impulses appear across the resistor 15. 'I'he capacitor 11 permits the relatively high frequency picture impulses to pass to the grid I4, while the synchronizing impulses at 16 and 1,000 cycles, respectively, are fed to the filter 33 by way of the leads 16.

In manufacturing the cathode ray tube, the ray-projector assembly, before insertion into the open neck of the tube II), includes the base portion 'I8 provided with a flange or rim I9 extending radially outwardly therefrom. After insertion of this assembly into the open neck of the tube, the edges of the rim I9 and the neck of the tube are fused together, the line of connection being indicated by the broken line 80 in Fig. 2. 'Ihe tube is then highly evacuated and sealed off.

By the term ray cut-off, as used in the claims, is meant the condition at which the electron ray is so diminished that no spot of light is perceptible on the screen structure 29.

I claim as my invention:

l. In a television receiving system, means for receiving transmitted picture impulses and amplifying, the same at radio frequency, detector apparatus connected to said means, said detector apparatus comprising a tube provided with fluorescent screen structure and an electron projector for` developing and focusing an electron beam on and directing the same toward said structure, and means for deilecting Said beam to cause the same to scan said structure.

2. The combination with a System for television reception comprising an electrical system for receiving a transmitted carrier wave modulated with picture impulses, a single piece of apparatus for detecting the picture impulses and utilizing the detected impulses to develop a picture; said apparatus including an electron projector comprising a cathode, an anode, and a control grid interposed between said cathode and anode; of an auxiliary electrode associated with said projector and arranged to substantially eliminate the effect of capacity-coupling between said grid and anode which would other- Wise occur in said system without the influence of said auxiliary electrode.

3. In a system for television reception, an electrical system for receiving a transmitted carrier wave modulated with picture and synchronizing impulses, and a single piece of apparatus in the form of an electron tube for detecting both the picture and synchronizing impulses and utilizing the detected picture impulses to develop a picture.

4. In a system for television reception, an electrical system for receiving a transmitted carrier wave modulated with picture impulses, a radio frequency amplifier for the received modulated carrier, and cathode ray apparatus having a control grid connected directly to said amplifier.

5. In a system for television reception, an electrical system for receiving a transmitted carrier wave modulated with picture impulses, and a single piece of apparatus in the form of an electron tube for detecting the picture impulses and utilizing the detected impulses to develop 8 picture.

VLADIMIR K. ZWORYKIN. 

